If you want "clean" (as in no Apistan or Checkmite) wax I've been buying mine from "fatbeeman" on Beesource. If you just want wax, you can buy it from Dadant, Brushy Mt etc. A local beekeeper, though, is your best bet since you won't have to pay the shipping. Cappings are usually pretty clean since the chemicals SHOULD only be in the brood nest and they should be new wax from this year. You can even melt down some 5.4mm foundation.
That's what I figure it's good for.